在linq查询中将nullable int转换为int返回匿名类型

Question

here simple linq to entities query that return anonymous type . The problem is that one of the int? values used like parameter to get another value that is int .

All ways that I know is not working. Please advise how to solve this problem.

public IQueryable<toursistdata> GetxTouristByCategory(string category)
        {
            var now = System.DateTime.MinValue;
            int i;
            switch (category)
            {
                case "arrival":
                    now = System.DateTime.Now.AddDays(-3);
                    var arrival = from a in db.xTourist
                                  where a.ArrDate >= now && a.Room == null
                                  select new toursistdata
                                  {
                                      kodt = a.Kod,
                                      name = a.Name,
                                      paxad = a.Paxad,
                                      paxch = a.Paxch,
                                      **//Here is h.Kod is int but KodH is int?**
                                      hotel = (from h in db.Address where h.Kod = (int)a.KodH.HasValue select h.NameC).FirstOrDefault(),
                                      room = a.Room,
                                      arrdate = a.ArrDate,
                                      arrtime = a.ArrTime,
                                      arrflight = a.ArrFl,
                                      depdate = a.DepDate,
                                      deptime = a.Deptime,
                                      depflight = a.DepFlight,
                                      transfer = a.Transfer
                                  };
                                  return arrival;
                case "inhouse":
                    now = System.DateTime.Today;
                    //return db.xTourist.AsQueryable().Where(p => p.Датапр >= now && p.Номер != null).OrderByDescending(p => p.Датапр);
                default:
                    //return db.xTourist.AsQueryable();
            }
        }

Answer 1

First there is one '=' missing in your equals operator. Then, if You want to compare an int with an int? you can use the Null Coalescing operator ?? to provide a default value for the null-case , then cast it to an int :

h.Kod == (a.KodH ?? 0)

Answer 2

The faulty line should read

• If you're sure the nullable int has a value

from h in db.Адреса where h.Kod = a.KodH.Value select h.NameC).FirstOrDefault()

• or if the nullable can be null then use a default value

from h in db.Адреса where h.Kod = (a.KodH ?? -1) select h.NameC).FirstOrDefault()

-or-

from h in db.Адреса where a.KodH!= null && h.Kod= a.KodH.Value select h.NameC).FirstOrDefault()

For more details on working with nullable types refer to MSDN Documentation